A printing ink is generally formulated according to strict performance requirements demanded by the intended market application and desired properties. Whether formulated for office printing or for production printing, particular ink is expected to produce images that are robust and durable under stress conditions.
In a typical design of a piezoelectric inkjet printing device, the image is applied by jetting appropriately colored inks during four to six rotations (incremental movements) of a substrate (an image receiving member or intermediate transfer member) with respect to the ink jetting head, i.e., there is a small translation of the printhead with respect to the substrate in between each rotation. This approach simplifies the printhead design, and the small movements ensure good droplet registration. At the jet operating temperature, droplets of liquid ink are ejected from the printing device and, when the ink droplets contact the surface of the recording substrate, either directly or via an intermediate heated transfer belt or drum, they quickly solidify to form a predetermined pattern of solidified ink drops.
Hot melt inks typically used with inkjet printers have a wax based ink vehicle, e.g., a crystalline wax. Such solid inkjet inks provide vivid color images. In typical systems, these crystalline wax inks partially cool on an intermediate transfer member and are then pressed into the image receiving medium such as paper. Transfuse spreads the image droplet, providing a richer color and lower pile height. The low flow of the solid ink also prevents show through on the paper.
However, the use of crystalline waxes places limitations on the printing process. First, the printhead must be kept at about 130° C. during the print process. Moreover, when the printhead is cooled and re-warmed, the resulting contraction and expansion of the ink requires a purge cycle to achieve optimum printhead performance. Furthermore, increased mechanical robustness is desired.
While known compositions and processes are suitable for their intended purposes, a need remains for improvements in ink compositions, for example with respect to jetting temperatures and image quality.
Recently, the assignee has discovered several radiation-curable inks that achieve more robust images following curing. Reference is made to the following patent properties, each of which is incorporated herein by reference in its entirety.
(1) Co-pending application Ser. No. 11/034,850 filed Jan. 14, 2005; (2) Co-pending application Ser. No. 11/034,856 filed Jan. 14, 2005; (3) Co-pending application Ser. No. 11/034,714 filed Jan. 14, 2005; (4) Co-pending application Ser. No. 11/018,378 filed Dec. 22, 2004; and (5) Co-pending application Ser. No. 11/034,866 filed Jan. 14, 2005.
Pigments are a robust class of colorants useful in a variety of applications such as, for example, paints, plastics and inks. Dyes have typically been the colorants of choice for inkjet printing inks because they are readily soluble colorants which enable jetting of the ink. Dyes have also offered superior and brilliant color quality with an expansive color gamut for inks, when compared to conventional pigments. However, since dyes are molecularly dissolved in the ink vehicle, they are often susceptible to unwanted interactions that lead to poor ink performance, for example photooxidation from light (will lead to poor lightfastness), dye diffusion from the ink into paper or other substrates (will lead to poor image quality and showthrough), and the ability for the dye to leach into another solvent that makes contact with the image (will lead to poor water-/solvent-fastness). In certain situations, pigments are the better alternative as colorants for inkjet printing inks since they are insoluble and cannot be molecularly dissolved within the ink matrix, and therefore do not experience colorant diffusion. Pigments may often be less expensive than dyes and are also attractive colorants for use in printing inks.
Key challenges with using pigments for inkjet inks are their large particle sizes and wide particle size distribution, the combination of which may pose critical problems with reliable jetting of the ink (i.e. inkjet nozzles are easily blocked). Pigments are rarely obtained in the form of single crystal particles, but rather as large aggregates of crystals and with wide distribution of aggregate sizes. The color characteristics of the pigment aggregate may vary widely depending on the aggregate size and crystal morphology. Thus, an ideal colorant that is widely applicable in, for example, inks and toners, is one that possesses the best properties of both dyes and pigments, namely: 1) superior coloristic properties (large color gamut, brilliance, hues, vivid color); 2) color stability and durability (thermal, light, chemical and air-stable colorants); 3) minimal or no colorant migration; 4) processable colorants (easy to disperse and stabilize in a matrix); and 5) inexpensive material cost. Thus, there is a need addressed by embodiments of the present invention, for smaller nano-sized pigment particles that minimize or avoid the problems associated with conventional larger-sized pigment particles. There further remains a need for processes for making and using such improved nano-sized pigment particles as colorant materials. The present nanosized pigment particles are useful in, for example, paints, coatings and inks (e.g., inkjet printing inks) and including radiation-curable compositions for inks and coatings, and other compositions where pigments may be used such as plastics, optoelectronic imaging components, photographic components, and cosmetics among others.
U.S. Patent Application Publication No. 2005/0109240 describes a method of producing a fine particle of an organic pigment, containing the steps of: flowing a solution of an organic pigment dissolved in an alkaline or acidic aqueous medium, through a channel which provides a laminar flow; and changing a pH of the solution in the course of the laminar flow.
WO 2006/132443 A1 describes a method of producing organic pigment fine particles by allowing two or more solutions, at least one of which is an organic pigment solution in which an organic pigment is dissolved, to flow through a microchannel, the organic pigment solution flows through the microchannel in a non-laminar state. Accordingly, the contact area of solutions per unit time may be increased and the length of diffusion mixing may be shortened, and thus instantaneous mixing of solutions becomes possible. As a result, nanometer-scale monodisperse organic pigment fine particles may be produced in a stable manner.
K. Balaklishnan et al., “Effect of Side-Chain Substituents on Self-Assembly of Perylene Diimide Molecules: Morphology Control,” J. Am. Chem. Soc., vol. 128, p. 7390-98 (2006) describes the use of covalently-linked aliphatic side-chain substituents that were functionalized onto perylene diimide molecules so as to modulate the self-assembly of molecules and generate distinct nanoparticle morphologies (nano-belts to nano-spheres), which in turn impacted the electronic properties of the material. The side-chain substituents studied were linear dodecyl chain, and a long branched nonyldecyl chain, the latter substituent leading to the more compact, spherical nanoparticle.
WO 2006/011467 discloses a pigment, which is used, for example, in color image display devices and may form a blue pixel capable of providing a high level of bright saturation, particularly a refined pigment, which has bright hue and is excellent in pigment properties such as lightfastness, solvent resistance and heat resistance, and a process for producing the same, a pigment dispersion using the pigment, and an ink for a color filter. The pigment is a subphthalocyanine pigment that is prepared by converting subphthalocyanine of the specified formula, to a pigment, has diffraction peaks at least at diffraction angles (2θ) 7.0°, 12.3°, 20.4° and 23.4° in X-ray diffraction and an average particle diameter of 120 to 20 nm.
U.S. Patent Application Publication No. 2006/0063873 discloses a process for preparing nano water paint comprising the steps of: A. modifying the chemical property on the surface of nano particles by hydroxylation for forming hydroxyl groups at high density on the surface of the nano particles; B. forming self-assembly monolayers of low surface energy compounds on the nano particles by substituting the self-assembly monolayers for the hydroxyl groups on the nano particles for disintegrating the clusters of nano particles and for forming the self-assembly monolayers homogeneously on the surface of the nano particles; and C. blending or mixing the nano particles having self-assembly monolayers formed thereon with organic paint to form nano water paint.
WO 2006/024103 discloses nanopigments prepared from organic IR dye and Na-bentonite with CEC of 95 mmole Na per 100 g of bentonite, at room temperature, by dissolving the Na-bentonite in water and mixing for 2 hours, and mixing in the dye, dissolved in ethanol, for 18 hours. The precipitate is filtered, washed three times with water/ethanol mixture, dried at 105° C. for 10 hours, and milled in a kitchen miller for 2 mins. 0.3 parts of the nanopigments were mixed to 100 parts of pulverized SPG resin and processed in an extruder with a die temperature of 190° C. to form transparent, faintly green or grey colored extrudates which were used to press film of 0.4 mm thickness at 160° C. The films were used to prepare IR-active laminated glass. Near infrared absorption spectra of the glass structures were obtained in a Perkin-Elmer Spectrophotometer.
WO 2006/005521 discloses a photoprotective composition comprising, in a physiologically acceptable medium: a) at least one aqueous phase, b) at least hydrophilic metal oxide nanoparticles, c) at least one vinylpyrrolidone homopolymer. The reference also discloses the use of at least one vinylpyrrolidone homopolymer in a photoprotective composition comprising at least one aqueous phase and at least hydrophilic metal oxide nanoparticles for the purpose of reducing the whitening and/or of improving the stability of the said composition. (dispersibility of the nanoparticles in the aqueous phase).
WO 2006/005536 discloses a method for producing nanoparticles, in particular, pigment particles. Said method consists of the following steps: (i) a raw substance is passed into the gas phase, (ii) particles are produced by cooling or reacting the gaseous raw substance and (iii) an electrical charge is applied to the particles during the production of the particles in step (ii), in a device for producing nanoparticles. The disclosure further relates to a device for producing nanoparticles, comprising a supply line, which is used to transport the gas flow into the device, a particle producing and charging area in order to produce and charge nanoparticles at essentially the same time, and an evacuation line which is used to transport the charged nanoparticles from the particle producing and charging area.
Japanese Patent Application Publication No. JP 2005238342 A2 discloses irradiating ultrashort pulsed laser to organic bulk crystals dispersed in poor solvents to induce ablation by nonlinear absorption for crushing the crystals and recovering the resulting dispersions of scattered particles. The particles with average size approximately 10 nm are obtained without dispersants or grinding agents for contamination prevention and are suitable for pigments, pharmaceuticals, etc.
U.S. Patent Application Publication No. 2003/0199608 discloses a functional material comprising fine coloring particles having an average primary particle diameter of 1 to 50 nm in a dried state, and having a BET specific surface area value of 30 to 500 m.sup.2/g and a light transmittance of not less than 80%. The functional material composed of fine coloring particles, exhibits not only an excellent transparency but also a high tinting strength and a clear hue.
U.S. Pat. No. 6,837,918 discloses a process and apparatus that collects pigment nanoparticles by forming a vapor of a pigment that is solid at room temperature, the vapor of the pigment being provided in an inert gaseous carrying medium. At least some of the pigment is solidified within the gaseous stream. The gaseous stream and pigment material is moved in a gaseous carrying environment into or through a dry mechanical pumping system. While the particles are within the dry mechanical pumping system or after the nanoparticles have moved through the dry pumping system, the pigment material and nanoparticles are contacted with an inert liquid collecting medium.
U.S. Pat. No. 6,537,364 discloses a process for the fine division of pigments which comprises dissolving coarsely crystalline crude pigments in a solvent and precipitating them with a liquid precipitation medium by spraying the pigment solution and the precipitation medium through nozzles to a point of conjoint collision in a reactor chamber enclosed by a housing in a microjet reactor, a gas or an evaporating liquid being passed into the reactor chamber through an opening in the housing for the purpose of maintaining a gas atmosphere in the reactor chamber, and the resulting pigment suspension and the gas or the evaporated liquid being removed from the reactor through a further opening in the housing by means of overpressure on the gas entry side or underpressure on the product and gas exit side.
U.S. Pat. No. 5,679,138 discloses a process for making inkjet inks, comprising the steps of: (A) providing an organic pigment dispersion containing a pigment, a carrier for the pigment and a dispersant; (B) mixing the pigment dispersion with rigid milling media having an average particle size less than 100 μm; (C) introducing the mixture of step (B) into a high speed mill; (D) milling the mixture from step (C) until a pigment particle size distribution is obtained wherein 90% by weight of the pigment particles have a size less than 100 nanometers (nm); (E) separating the milling media from the mixture milled in step (D); and (F) diluting the mixture from step (E) to obtain an inkjet ink having a pigment concentration suitable for inkjet printers.
Japanese Patent Application Publications Nos. JP 2007023168 and JP 2007023169 discloses providing a pigment dispersion compound excellent in dispersibility and flowability used for the color filter which has high contrast and weatherability. The solution of the organic material, for example, the organic pigment, dissolved in a good solvent under the existence of alkali soluble binder (A) which has an acidic group, and a poor solvent which makes the phase change to the solvent are mixed. The pigment nanoparticles dispersed compound re-decentralized in the organic solvent containing the alkali soluble binder (B) which concentrates the organic pigment nanoparticles which formed the organic pigment as the particles of particle size less than 1 μm, and further has the acidic group.
Kazuyuki Hayashi et al., “Uniformed nano-downsizing of organic pigments through core-shell structuring,” Journal of Materials Chemistry, 17 (6), 527-530 (2007) discloses that mechanical dry milling of organic pigments in the presence of mono-dispersed silica nanoparticles gave core-shell hybrid pigments with uniform size and shape reflecting those of the inorganic particles, in striking contrast to conventional milling as a breakdown process, which results in limited size reduction and wide size distribution.
U.S. Patent Application Publication No. 2007/0012221 describes a method of producing an organic pigment dispersion liquid, which has the steps of: providing an alkaline or acidic solution with an organic pigment dissolved therein and an aqueous medium, wherein a polymerizable compound is contained in at least one of the organic pigment solution and the aqueous medium; mixing the organic pigment solution and the aqueous medium; and thereby forming the pigment as fine particles; then polymerizing the polymerizable compound to form a polymer immobile from the pigment fine particles.
The appropriate components and process aspects of each of the foregoing may be selected for the present disclosure in embodiments thereof and the entire disclosure of the above-mentioned references are totally incorporated herein by reference.
Fluorescent inks and toners are among the most widely used security printing features. A printed document is usually authenticated by detecting the light emitted by the fluorescent component when subjected to black light. The light emitting property cannot be reproduced in a second generation copy.
Fluorescent dyes used in fluorescent inks and toners can lose fluorescence in the print-head when the ink is heated to a temperature greater than 120° C. to melt during normal operation. To overcome this problem, the security printing industry uses hard, robust pigments containing the dye of interest. Pigments are preferred over fluorescent dyes because of their improved chemical, light fastening and thermal stability. Pigments are also preferred by the industry because there is limited or no migration or bleeding of the dye compound.
Most commercially available fluorescent pigments are made by grinding a bulk polymer matrix containing fluorescent materials. This process does not result in fluorescent particles of a size smaller than 1-2 microns, and typically the size of these particles is about 4-5 microns. According to this process, fluorescent dyes are incorporated into hard, crosslinked particles, thereby limiting the mobility of the fluorescent dye. Once the fluorescent dye is isolated from interaction with other materials present in the ink and, chemical degradation by the environment is diminished. These hard particles are dispersed in the marking material, typically liquid inks.
Inks based on fluorescent pigments are currently used in rotogravure, flexographic, silk-screening and off-set printing systems. However, given their large size, inks based on these pigments cannot be used with inkjet, solid ink or UV curable inks, because they physically clog the inkjet nozzles.
Thus, there is a need for fluorescent compositions, including fluorescent compositions that may be used in/with inkjet inks, solid inks, UV curable inks and EA (Emulsion Aggregation) toners and that have suitable thermal degradation properties. There is a further need for fluorescent compositions of such small size that may be used in/with inkjet inks, solid inks, UV curable inks and EA toners that are compatible with organic based marking materials.
The present disclosure addresses these needs by providing UV curable inks, particularly radiation curable compositions containing at least one nanoscale fluorescent pigment particle and/or at least one fluorescent organic nanoparticle, and the use of such inks in methods for forming images, particularly their use in inkjet printing.